LUCENE-6343: DefaultSimilarity javadocs has the wrong example for encode/decode precision loss

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1664687 13f79535-47bb-0310-9956-ffa450edef68

lucene/CHANGES.txt

@@ -223,6 +223,9 @@ Other
 * LUCENE-6333: Refactored queries to delegate their equals and hashcode
   impls to the super class. (Lee Hinman via Adrien Grand)
 
+* LUCENE-6343: DefaultSimilarity javadocs had the wrong float value to
+  demonstrate precision of encoded norms (András Péteri via Mike McCandless)
+
 Changes in Runtime Behavior
 
 * LUCENE-6255: PhraseQuery now ignores leading holes and requires that

lucene/core/src/java/org/apache/lucene/search/similarities/DefaultSimilarity.java

@@ -29,7 +29,7 @@ import org.apache.lucene.util.SmallFloat;
  * {@link #decodeNormValue(long) decoded} back to a float <i>norm</i> value.
  * This encoding/decoding, while reducing index size, comes with the price of
  * precision loss - it is not guaranteed that <i>decode(encode(x)) = x</i>. For
- * instance, <i>decode(encode(0.89)) = 0.75</i>.
+ * instance, <i>decode(encode(0.89)) = 0.875</i>.
  * <p>
  * Compression of norm values to a single byte saves memory at search time,
  * because once a field is referenced at search time, its norms - for all

lucene/core/src/test/org/apache/lucene/search/similarities/TestDefaultSimilarity.java

@@ -0,0 +1,30 @@
+package org.apache.lucene.search.similarities;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import org.apache.lucene.util.LuceneTestCase;
+
+public class TestDefaultSimilarity extends LuceneTestCase {
+
+  // Javadocs give this as an example so we test to make sure it's correct:
+  public void testPrecisionLoss() throws Exception {
+    DefaultSimilarity sim = new DefaultSimilarity();
+    float v = sim.decodeNormValue(sim.encodeNormValue(.89f));
+    assertEquals(0.875f, v, 0.0001f);
+  }
+}